Consideration of petrographic and U-Pb provenance data and paleocurrent analysis of Kungurian (upper Leonardian) Cutler Group strata in the salt anticline province of the Paradox Basin of Utah demonstrates striking contrasts in composition and inferred sources of stratigraphically adjacent eolian and fluvial facies. Eolian strata, termed here the Castle Valley Sandstone, exposed in the Castle Valley northeast of Moab, Utah, and long correlated with the White Rim Sandstone, were deposited on the southwestern flank of a NW-trending diapiric salt wall. The eolian strata, which overlie red fluvial sandstone and conglomerate of the undifferentiated Cutler Formation, are as much as 183 m thick in outcrop and consist of two eolianite members separated by a thin sheet-flood deposit that contains pebbles derived from the salt wall and upturned conglomeratic strata adjacent to it. Both eolian and underlying fluvial deposits thin and onlap eastward onto the now-collapsed salt wall. Fluvial strata at Castle Valley and in exposures to the northeast were transported northwestward, parallel to the salt wall. Large-scale foresets in the lower eolianite member indicate dominant northeasterly wind directions (present coordinates) and transport directly away from the contemporary Uncompahgre uplift, whereas foresets in the upper member indicate variable northeasterly and northwesterly paleowinds. The eolian strata thus accumulated on the lee side of the salt wall, but sandstone composition and northwesterly wind components indicate net transport from the northwest, comparable with dominant southeastward sand transport, away from the Pangean shoreline, documented for the greater White Rim erg to the west and northwest. The NW and NE winds are both predicted by late Paleozoic atmospheric circulation models for western Pangea.
Cutler fluvial sandstones are compositional arkoses (mean Qt56F42L2) containing basement-derived detrital components that include potassium feldspar, plagioclase, biotite, and zircons with a restricted, bimodal age distribution of ∼1790–1689 Ma and ∼1466–1406 Ma. These grain ages exactly match known basement ages in the nearby Uncompahgre uplift. In contrast, the Castle Valley Sandstone ranges from quartz-rich arkose to subarkose and exhibits a consistent upsection decrease in feldspar content, from Qt71F27L2 in the lower eolianite member to Qt90F10L0 in the upper member. Like the underlying fluvial arkose, the lower eolianite member contains potassium feldspar, plagioclase, and mica derived from the Uncompahgre uplift, but the locally derived zircon age groups constitute only 23%–37% and 13% of the zircon grain ages in the lower and upper eolianite members, respectively; whereas older Archean and Paleoproterozoic grains, including ca. 1.5 Ga grains uncommon in the Laurentian detrital-zircon record, and Grenville, Neoproterozoic, and early Paleozoic grains constitute the bulk of the zircons. Quartzarenite of the greater White Rim erg contains detrital-zircon populations similar to those of the upper eolianite member. The Grenville and younger grains are interpreted as having an eastern Laurentian (Appalachian) source, whereas the ca. 1.5 Ga grains probably had an ultimate source in Baltica. Sediment-transport directions indicate that zircon grains not directly attributable to local basement of the Ancestral Rocky Mountains, including grains with a likely Baltica source, were transported to the western shoreline of Laurentia by transcontinental fluvial systems and then southeastward to their depositional site at the erg margin in salt-withdrawal minibasins.
- Received 3 February 2015.
- Revision received 17 April 2015.
- Accepted 18 June 2015.
- © Geological Society of America